Damage to and loss of neurons and axons is correlated with disability in multiple sclerosis (MS), thus neuroprotective therapies are urgently needed. In previous studies we have found altered expression of mitochondrial genes and proteins involved in respiration resulting in dysfunctional mitochondrial activity in postmortem MS cortex. Recently, we have shown that hemoglobin is upregulated in MS cortex and have localized hemoglobin expression to neurons in the MS brain. We have also found hemoglobin expression in primary cultures of neurons isolated from rat brain. This is a surprising and novel finding and provides support for our hypothesis that hemoglobin expression may be involved in neuronal respiration. The goal of this study is to understand the function of hemoglobin expression in neurons and its significance to neuropathology in MS. In the proposed study we will investigate the extent and localization of hemoglobin expression in different regions of the MS brain by in situ hybridization, RT-PCR, western blotting, confocal imaging, and electron microscopy of postmortem MS and control tissue. We will investigate the mechanisms which regulate hemoglobin expression in primary neuronal cultures and will assess the role of hemoglobin in neuronal respiration and oxidative phosphorylation by performing high resolution respirometry on neuroblastoma cells expressing hemoglobin subunits from a mammalian expression vector, and on brain slices from mice treated with erythropoietin which increases hemoglobin expression in the brain. We will also investigate the possibility that hemoglobin serves a neuroprotective role in the brain as a scavenger of free radicals.